固体高分辨13C NMR研究γ线辐照对结晶聚乙稀聚集态结构的影响

结晶聚乙烯(PE)经⁶⁰Coγ线辐照后,用固体高分辨¹³C NMR CP/DD MAS方法观测解析了辐射效果与具有片晶结构的结晶相,结晶-橡胶状无定形界面相以及橡胶状无定形相的聚集态结构的关系。考察了各相中的¹³C核自旋-晶格弛豫和自旋-自旋弛豫行为及辐照对其影响。得到辐照后产生交联,破坏,相转变及晶型变化等有意义的结果,对PE的辐照效应和机制的探讨提供了核磁共振的新实验证据。     

Instability of a half-space with frictional materials

The instability of an initially compressed half-space which consists of dilatant frictional materials is examined. It is assumed that the material response is governed by elastoplastic constitutive relations that include plastic compressibility (or dilatancy) and frictional effects, and hence involves a nonassociative flow rule. Stability limits are established, and it is shown that (unlike for elastic materials) for this class of materials folding by surface instability can be initiated at compressive forces that are considerably smaller than the initial shear modulus. The results are illustrated in terms of some published data on certain sandstones.

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Zusammenfassung Die Instabilität eines zusammengedrückten Halbraumes aus kompressiblem Material mit Reibung wird untersucht. Das Material soll elastisch plastischen Stoffgleichungen mit plastischer Kompressibilität und Reibungseffekten genügen. Die Fließregel ist demzufolge nicht jene des plastischen Potentials. Die Stabilitätsgrenzen sind aufgeteilt, und es wird gezeigt, daß im Gegensatz zu elastischen Materialien die Deformation infolge der Oberflächeninstabilität für das vorliegende Stoffverhalten schon bei Druckspannungen entsteht, welche im Vergleich zum Anfangswert des Schubmodulus viel kleiner sind. Die Resultate sind mit Hilfe von bereits publizierten Kennwerten von gewissen Sandsteinen numerisch ausgewertet.

     

Combustion characteristics of Mg vapor jet flames in CO2 atmospheres

An experimental study was performed on the combustion characteristics of a jet diffusion flame of Mg vapor injected through a small nozzle into CO₂ atmospheres at low pressures from 8 to 48 kPa with a view to using Mg as fuel for a CO₂-breathing turbojet engine in the Mars atmosphere. The Mg vapor jet produced three types of the flame. At lower pressures and higher injection velocities, a red-heated jet flame formed, in which the injected Mg vapor was heated by spontaneous reactions, turning red. At medium pressures and injection velocities, a stable luminous lifted-like flame developed above the rim of the chimney, a tube-like combustion product for the Mg vapor passage that grew on the nozzle during combustion. The flame had similar flame length properties to laminar jet diffusion flames of gaseous fuels. At higher pressures and lower injection velocities, a stable luminous attached flame developed at the rim of the chimney. The same reactions, producing MgO(g), CO and MgO(c), proceeded preferentially for all flames and chimneys. Carbon was only subordinately generated. Burning behavior of Mg vapor jets in a CO₂ atmosphere has been represented, including the homogeneous reaction of Mg vapor with CO₂, the diffusion of CO₂, and the condensation and deposit of MgO. The injection velocity of Mg vapor at the rim of the chimney and the exothermic reactions with diffused CO₂ that occur there play a crucial role in the attachment and development of the flames. The flame structure may be explained in terms of the relatively low gas-phase reaction rate of Mg with CO₂.     

Synthesis of Anisotropic Hydrogels and Their Applications

Owing to their water‐rich structures, which are similar to those of biological tissues, hydrogels have long been regarded as promising scaffolds for artificial tissues and organs. However, in terms of the structural anisotropy, most synthetic hydrogels are substantially different from biological systems. Synthetic hydrogels are usually composed of randomly oriented three‐dimensional polymer networks whereas biological systems adopt anisotropic structures with hierarchically integrated building units. Such anisotropic structures often play essential roles in biological systems to exhibit particular functions. In this context, anisotropic hydrogels provide an entry point for exploring biomimetic applications of hydrogels. Reflecting these aspects, an increasing number of studies on anisotropic hydrogels have been reported recently. This Minireview highlights the use and perspectives of these anisotropic hydrogels, particularly focusing on their preparation, structures, and applications.     

Extra‐Large Mechanical Anisotropy of a Hydrogel with Maximized Electrostatic Repulsion between Cofacially Aligned 2D Electrolytes

In our previous work, we have shown that “electrostatic forces”, when generated anisotropically in aqueous media by 2D electrolytes upon cofacial orientation, enable the formation of a hydrogel with an anisotropic parameter, as defined by the ratio of elastic moduli E_⊥/E_∥, of 3.0. Herein, we successfully developed the design strategy for a hydrogel with an anisotropic parameter of no less than 85. This value is not only 28 times greater than that of our previous anisotropic hydrogel but also 6 times larger than the current champion record in synthetic hydrogels (E_⊥/E_∥～15). Firstly, we simply lowered ionic contaminants in the hydrogel and were able to enhance the anisotropic parameter from 3.0 to 18. Then, we chose a supporting polymer network allowing the hydrogel to carry a higher interior permittivity. Consequently, the anisotropic parameter was further enhanced from 18 to 85. Owing to the enhanced mechanical anisotropy, our new hydrogel displayed a superb ability of seismic isolation.     

Monoterpenes produced by Cupressus lusitanica cultured cells including a novel monoterpene (1s, 2s, 6s)-(+)-1,6-epoxy-4(8)-p-menthen-2-ol

A novel monoterpene, (1S, 2S, 6S)-(+)-1,6-epoxy-4(8)-p-menthen-2-ol, was isolated from an elicitor-treated cell culture of Cupressus lusitanica (Mexican cypress). Ten known monoterpenes--limonene, myrcene, beta-ocimene, sabinene, terpinolene, 4-terpineol, alpha-terpineol, 4(8)-p-menthen-1,2-diol, 4-hydroxyphellandric acid methylester and beta-thujaplicin methylether--were also identified. Regioselective metabolisms of monoterpenes were observed in this culture.     

Absolute stereochemistry of securinine

The absolute configuration of securinine was shown to be I from the rotatory dispersion curves and molecular rotations of degradation products of securinine. The conclusion was unequivocally confirmed by the formation of (+)-N-benzoylpipecolic acid on degradation of this alkaloid. The conformation of the bridgehead nitrogen was also discussed.     

Reaction of glycidyl phenyl ether with imines: A model study of latent hardeners of epoxy resins in the presence of water

The hydrolyses of several imines and their reactions with glycidyl phenyl ether were examined under highly humid conditions as a model study for the development of water‐initiated hardeners for epoxy resins. Diethyl ketone‐based imines were hydrolyzed more efficiently than methyl isobutyl ketone‐based imines. The reactions of glycidyl phenyl ether with the imines depended on their hydrolysis rates and the basicity of the amines generated from them. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 971–975, 2002